1. Field of the Invention
The present invention relates to an electron-emitting device, an electron-emitting apparatus, an electron source and an image-forming apparatus. The present invention also relates to a display apparatus such as a television broadcast display, a display for use in a video conference system or a computer display, and to an image-forming apparatus designed as an optical printer using a photosensitive drum or the like.
2. Related Background Art
A field emission (FE) type of electron-emitting device which emits electrons from a surface of a metal when a strong electric field of 106 V/cm or higher is applied to the metal, and which is one of the known cold cathode electron sources, is attracting attention.
If the FE-type cold electron source is put to practical use, a thin emissive type image display apparatus can be realized. The FE-type cold electron source also contributes to reductions in power consumption and weight of an image display apparatus.
FIG. 13 shows a vertical FE-type cold electron source structure formed of a substrate 131, an emitter electrode 132, an insulating layer 133, an emitter 135, and an anode 136. The shape of an electron beam with which the anode is irradiated is indicated by 137. This structure is of a Spindt type such that an opening is formed in the insulating layer 133 and the gate electrode 134 provided on the cathode 132, and the emitter 135 having a conical shape is placed in the opening. (This type of structure is disclosed by, for example, C. A. Spindt, “Physical Properties of thin-film field emission cathodes with molybdenum cones”, J. Appl. Phys., 47, 5248 (1976).)
FIG. 14 shows a lateral FE structure formed of a substrate 141, an emitter electrode 142, an insulating layer 143, an emitter 145, and an anode 146. The shape of an electron beam with which the anode is irradiated is indicated by 147. The emitter 145 having an acute extreme end and the gate electrode 144 for drawing out electrons from the extreme end of the emitter are disposed above and parallel to the substrate, and the collector (anode) is formed above the gate electrode and the emitter electrode remote from the substrate (see U.S. Pat. Nos. 4,728,851, 4,904,895, etc.).
Also, Japanese Patent Application Laid-open No. 8-115652 discloses an electron-emitting device using fibrous carbon which is deposited in a narrow gap by performing thermal cracking of an organic chemical compound gas on a catalyst metal.
In an image display apparatus using one of the above-described FE-type electron sources, an electron beam spot is obtained which has a size (hereinafter referred to as “beam diameter”) depending on the distance H between the electron source and the phosphor, the anode voltage Va, and the device drive voltage Vf. The beam diameter is smaller than a millimeter and the image display apparatus has sufficiently high resolution.
In recent years, however, there has been a tendency to require higher resolution of image display apparatuses.
Further, with the increase in the number of display pixels, power consumption during driving due to the device capacitance of electron-emitting devices is increased. Therefore there is a need to reduce the device capacitance and the drive voltage and to improve the efficiency of electron-emitting devices.
In the above-described Spindt type of electron source, the gate is laminated on the substrate with the insulating layer interposed therebetween, so that parasitic capacitances are produced between large capacitances and a multiplicity of emitters. Moreover, the drive voltage is high, several ten to several hundred volts, and capacitive power consumption is disadvantageously large because of the specific structure.
Also, since the beam of electrons drawn out spreads out, there is a need for a focusing electrode for limiting spreading of the beam. For example, Japanese Patent Application Laid-open No. 7-6714 discloses a method of converging electron trajectories by disposing an electrode for focusing electrons. This method, however, has the problem of an increase in complexity of the manufacturing process, a reduction in electron emission efficiency, etc., due to the addition of the focusing electrode.
In ordinary lateral FE electron sources, electrons emitted from the cathode are liable to impinge on the opposed gate electrode. Therefore the structure of lateral FE electron sources has the problem of a reduction in the efficiency (the ratio of the electron current flowing through the gate and the electron current reaching the anode) and considerable spreading of the beam shape on the anode.